title: High precision transponder localization using a novel electromagnetic positioning system in patients with localized prostate cancer.
abstract: OBJECTIVE
  The Micropos 4DRT system is being developed to provide accurate, precise, objective, and continuous target localization during radiotherapy. This study involves the first in vivo use of the system, aiming to evaluate the localization accuracy of this electromagnetic positioning technique compared with radiographic localization and to assess its real-time tracking ability.
  
  
  METHODS
  An active positioning marker was inserted in the prostatic urethra of 10 patients scheduled to receive radiotherapy for localized prostate cancer. A receiving sensor plate (antennae system) was placed at a known position in the treatment tabletop. Initial in vivo system calibrations were performed in three subjects. Ten additional patients were then enrolled in a study arm that compared radiographic transponder location to radiotransponder location simultaneously acquired by the Micropos 4DRT system. Frontal and side radiographs were taken with the radiopaque transponder located at three different positions within the prostatic urethra.
  
  
  RESULTS
  The transponder insertions were all successful and without complications. Comparison of the transponder location as per the Micropos 4DRT system with the radiographic transponder localization showed an average (+/-SD) absolute and relative 3D difference of 2.7+/-1.2 and 1.7+/-1.0mm, respectively. Continuous transponder tracking capability was also demonstrated.
  
  
  CONCLUSIONS
  Electromagnetic positioning using the Micropos transponder system is feasible in vivo. Evaluation of this novel non-ionizing localization system, in this study using a transponder positioned in the prostatic urethra, indicates transponder localization accuracy to isocenter comparable with X-ray localization of a radiopaque marker.
authors.affiliation: Department of Oncology, Sahlgrenska University Hospital, Gothenburg, Sweden. jon.kindblom@oncology.gu.se
authors.forename: Jon
authors.initials: J
authors.lastname: Kindblom
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Ekelund-Olvenmark
authors.forename: Hanna
authors.initials: H
authors.lastname: Syren
authors.forename: Roman
authors.initials: R
authors.lastname: Iustin
authors.forename: Karin
authors.initials: K
authors.lastname: Braide
authors.forename: Ingela
authors.initials: I
authors.lastname: Frank-Lissbrant
authors.forename: Bo
authors.initials: B
authors.lastname: Lennernäs
mesh_terms: D055590:Electromagnetic Phenomena; D006801:Humans; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000379:methods*